Biocompatibie polyanhydride linkers having improved degradation properties for use in the production of drug polymers have now been developed. These linkers serve as the polymeric backbone of degradable polymer drug delivery systems for a multitude of low molecular weight drugs which comprise within their structure one carboxylic acid group as well as at least one amine, thiol, alcohol or phenol group. Drug polymers linked via these biocompatible, biodegradable polyanhydrides can be administered to a host by a variety of routes including, but not limited to orally, subcutaneously, intramuscularly, intradermally and topically, depending upon the drug linked via the polyanhydride and the selected use for the drug.
Polymers comprising aromatic or aliphatic anhydrides have been studied extensively over the years for a variety of uses. For example, in the 1930s fibers comprising aliphatic polyanhydrides were prepared for use in the textile industry. In the mid 1950s, aromatic polyanhydrides were prepared with improved film and fiber forming properties. More recently, attempts have been made to synthesize polyanhydrides with greater thermal and hydrolytic stability and sustained drug release properties.
U.S. Pat. Nos. 4,757,128 and 4,997,904 disclose the preparation of polyanhydrides with improved sustained drug release properties from pure, isolated prepolymers of diacids and acetic acid. However, these biocompatible and biodegradable aromatic polyanhydrides have radical or aliphatic bonds resulting in compounds with slow degradation times as well as relatively insoluble degradation products unless incorporated into a copolymer containing a more hydrophilic monomer, such as sebacic acid. The aromatic polyanhydrides disclosed in the ""128 Patent and the ""904 Patent are also insoluble in most organic solvents. A bioerodible controlled release device produced as a homogenous polymeric matrix from polyanhydrides with aliphatic bonds having weight average molecular weights greater than 20,000 and an intrinsic velocity greater than 0.3 dL/g and a biologically active substance is also described in U.S. Pat. No. 4,888,176. Another bioerodible matrix material for controlled delivery of bioactive compounds comprising polyanhydride polymers with a uniform distribution of aliphatic and aromatic residues is disclosed in U.S. Pat. No. 4,857,311.
Biocompatible and biodegradable aromatic polyanhydrides prepared from para-substituted bis-aromatic dicarboxylic acids for use in wound closure devices are disclosed in U.S. Pat. No. 5,264,540. However, these compounds exhibit high melt and glass transition temperatures and decreased solubility, thus making them difficult to process. The disclosed polyanhydrides also comprise radical or aliphatic bonds which can not be hydrolyzed by water.
Polyanhydride polymeric matrices have also been described for use in orthopedic and dental applications. For example, U.S. Pat. No. 4,886,870 discloses a bioerodible article useful for prosthesis and implantation which comprises a biocompatible, hydrophobic polyanhydride matrix. U.S. Pat. No. 5,902,599 also discloses biodegradable polymer networks for use in a variety of dental and orthopedic applications which are formed by polymerizing anhydride prepolymers.
Biocompatible and biodegradable polyanhydrides have now been developed with improved degradation, processing and solubility properties, as well as utilities based upon their degradation products.
An object of the present invention is to provide biocompatible and biodegradable polyanhydrides which serve as the polymeric backbone linking drug molecules into polymeric drug delivery systems. These polyanhydrides demonstrate enhanced solubility and processability, as well as degradation properties due to the use of hydrolyzable bonds such as esters, amides, urethanes, carbamates and carbonates as opposed to radical or aliphatic bonds. The polyanhydride linker of the present invention comprises the structure of Formula I: 
wherein R1 is selected from the group consisting of alkyls, cycloalkyls, substituted alkyls, aromatics, substituted aromatics, lactams, and lactones; X is selected from the group consisting of amides, thioamides, esters and thioesters; and R2 is an alkyl represented by xe2x80x94(CH2)n wherein n is from 1 to 20.
This polyanhydride is used to link low molecular weight drug molecules comprising within their molecular structure one carboxylic acid group and at least one amine, thiol, alcohol or phenol group. Accordingly, polyanhydrides of Formula (I) serve as the polymer backbone of polymeric drug delivery systems comprising these low molecular weight drugs.
Thus, the present invention also relates to compositions, methods of producing compositions and methods of using compositions comprising a polyanhydride of Formula (I) and low molecular weight drug molecules containing within their structure one carboxylic acid group and at least one amine, thiol, alcohol or phenol group, wherein molecules of the drug are linked to one another via the polyanhydride. These polymeric drug delivery systems provide an effective means to deliver drugs in a controlled fashion to any site of a host. By xe2x80x9chostxe2x80x9d it is meant to include both animals and plants.